1. Field of the Invention
The present invention relates to an image pick-up device unit having an image pick-up device for obtaining an image signal corresponding to light irradiated on a photoelectrically converting surface or a camera having the image pick-up device unit. More particularly, the present invention relates to the improvement of a camera, such as an interchangeable single-lens reflex digital camera.
2. Related Background Art
Recently, digital cameras such as a so-called digital still camera or a digital video camera (hereinafter, referred to as a digital camera or simply referred to as a camera) are generally put into practical use and are widely spread. In the digital cameras, a subject image formed subject beams), which are transmitted through a photographing optical system (also referred to as a photographing lens) is formed onto a photoelectrically converting surface of a solid image pick-up device arranged at a predetermined position, such as a CCD (Charge Coupled Device, hereinafter, simply referred to as an image pick-up device). Further, an electrical image signal or the like representing a desired subject image is generated by using an photoelectrically converting action of the image pick-up devices. A signal based on the image signal and the like are outputted to a predetermined display device such as an LCD (Liquid Crystal Display) and an image or the like is displayed. The image signal or the like generated by the image pick-up device is recorded to a predetermined recording area of a predetermined recording medium as predetermined-format image data. Further, the image data recorded to the recording medium is read and the image data is converted to become an image signal which is optimum for a display using the display device. Thereafter, an image corresponding thereto is displayed based on the processed image signal.
In general, digital cameras have an optical finder device for observing, prior to a photographing operation, a desired subject as a photographing target and for setting a photographing range including the subject.
In general, a so-called single-lens reflex finder device is used as the optical finder device. In this single-lens reflex finder device, the advancing direction of the subject beams transmitted through the photographing optical system is bent by using a reflecting member arranged on the optical axis of the photographing optical system such that the subject image for observation is formed at a predetermined position. On the other hand, upon the photographing operation, the reflecting member is evacuated from the optical axis of the photographing optical system, thereby guiding the subject beams onto a light receiving surface of the image pick-up device, that is, onto a photoelectrically converting surface thereof and forming the subject image for photographing on the photographically converting surface.
Furthermore, recently, a so-called interchangeable lens digital camera having the single-lens reflex finder device is generally put into practical use. In the interchangeable lens digital camera, the photographing optical system is detachable to a camera main body, and a plurality of types of the photographing optical systems are selectively used in the single-camera main body by arbitrarily detaching and exchanging a desired photographing optical system in accordance with user's desire.
In the above-mentioned interchangeable lens digital camera, dust and the like floating in the air possibly enter the camera main body upon detaching the photographing optical system from the camera main body. Various mechanisms which are mechanically operated such as a shutter and a stop mechanism are arranged in the camera main body and thus, dust is possibly generated from the various mechanisms during the operation.
Upon detaching the photographing optical system from the camera main body, the light receiving surface (also referred to as the photoelectrically converting surface) of the image pick-up device arranged in the rear of the photographing optical system is exposed in the ambient air of the camera. Therefore, dust and the like are adhered to the photographing converting surface of the image pick-up device due to electric charge action and the like.
Further, the conventional digital camera having the interchangeable lens generally include various optical members, such as a protecting glass for protecting a light receiving surface of the image pick-up device, an optical low-pass filter, and an infrared cut-off filter, in a space between the photoelectrically converting surface and the photographing optical system. Therefore, the above-mentioned dust, etc. is adhered to the surfaces of the various optical members.
In the conventional digital cameras, when the dust, etc. is adhered to the photoelectrically converting surface of the image pick-up device or the surfaces of the various optical members, a part of subject beams which are transmitted through the photographing optical system and which reach the photoelectrically converting surface of the image pick-up device is shielded by the dust, etc. Thus, a predetermined shadow is formed onto the photoelectrically converting surface. Then, the shadow due to the dust, etc. is photographed on the image based on the image signal obtained by the image pick-up device. This causes the deterioration in image quality.
Then, various means as a dust-proofing structure is proposed for the conventional digital cameras. For example, the dust-proofing structure prevents the entering of the dust, etc. in a space between the optical member and the photographically converting surface of the image pick-up device by constituting a sealing space which is sealed from the outside.
However, with the above dust-proofing structure, there is a possibility that dust, etc. can still be adhered to a surface in the foremost part of the unit, namely, on the arrangement side of the photographing optical system as an incident surface of the subject beams after being transmitted through the photographing optical system.
In particular, the digital cameras having the interchangeable lens generally use a focal plane type shutter mechanism arranged near the image pick-up device. However, the focal plane type shutter mechanism has many operating members and therefore dust, etc. is caused by operating the operating members.
Then, for example, Japanese Patent Publication No. 2809133 discloses means by which the image based on the obtained image signal is prevented from an adverse influence due to the adhesion of dust to the surface of the optical members provided in front of the image pick-up device (photoelectrically converting device).
In the image pick-up device unit disclosed in Japanese Patent Publication No. 2809133, the dimension of an interval between a beam incident surface and a light receiving surface (photoelectrically converting surface) of a photoelectrically converting device is regulated by a predetermined condition formula on a package (unit) which seals the photoelectrically converting device (image pick-up device). The dimension of the interval for satisfying the condition formula sets positions of the beam incident surface of the package and the light receiving surface of the photoelectrically converting device.
Consequently, if dust is adhered to the beam incident surface of the package, the influence from the shade formed by the dust to the optical image based on an electrical signal obtained by the photoelectrically converting device is suppressed.
The means disclosed in Japanese Patent Publication No. 2809133 is a technology which is applied to the package of the photoelectrically converting device for focal detection. This means is effective to obtain the optical image for the focal detection without trouble. However, the means cannot be applied to an image pick-up device unit of a camera such as a digital camera for obtaining the image signal indicating an image by the image pick-up device. That is, a trouble can be caused upon displaying the optical image based on the obtained image signal (image), even if the image signal is proper for a focal detecting accuracy.
Further, the means disclosed in Japanese Patent Publication No. 2809133 has the following problems because the size of the dust particles is not considered.
In other words, in the means disclosed in Japanese Patent Publication No. 2809133, the size of a shade formed by the dust, etc. adhered to the beam incident surface of the package is regulated by a predetermined calculating formula. In this case, the size of the shade formed by the dust, etc. is set to be 15 times or more of a pixel interval (pitch) of the photoelectrically converting device. Thus, the influence on the image formed on the light receiving surface of the photoelectrically converting device due to the shade is suppressed.
However, of course, the size of the shade formed by the dust depends on the size of the dust, etc. As the size of the dust increases, the shade is expanded more widely on the photoelectrically converting surface. In this case, the density of the shadow is not decreased. Therefore, the shade adversely influences on the image formed onto the light receiving surface of the photoelectrically converting device. The shade causes the deterioration in picture quality of the image based on the obtained image signal.
Namely, if the beam incident surface of the package is regulated in accordance with the dimension of the distance regulated by the means disclosed in Japanese Patent Publication No. 2809133, the shade formed by the dust adversely influences on the image depending on the size of the dust particles adhered to the beam incident surface.
On the contrary, in the means disclosed in Japanese Patent Publication No. 2809133, upon using the beam incident surface having the dimension of the interval between the beam incident surface of the package and the light receiving surface of the photoelectrically converting device, which is regulated by the above calculation, even when there is a possibility that the shade adversely influence on the image, no trouble can actually be caused depending on the size of the dust particles adhered to the beam incident surface.
The above-mentioned contradiction due to the usage of the means disclosed in Japanese Patent Publication No. 2809133 is caused because the size of the dust particles is not considered in the disclosed means.